The case against processed food just keeps getting stronger. But, amazingly, we still don’t understand exactly why it’s so bad for us.

In two papers published in the BMJ in May 2019the more ultraprocessed — or industrially manufactured — foods a person ate, the more likely they were to get sick and even die. In one study, they were more likely to suffer from cardiovascular problems. The other linked an ultraprocessed diet to a higher risk of death from all causes.

Those studies followed a first-of-its-kind randomized controlled trial, out of the National Institutes of Health: Researchers found people following an ultraprocessed diet ate about 500 more calories per day than those consuming minimally processed, whole foods. Then, a December paper in JAMA Internal Medicine found that the more ultraprocessed food a person ate, the higher their risk of Type 2 diabetes.

Sure, potato chips, cookies, and hot dogs are chock-full of salt, sugar, fat, and calories. They can cause us to gain weight and put us at a higher risk of diseases such as obesity.

But why? What if there’s something unique about ultraprocessed foods that primes us to overeat and leads to bad health?

A new, intriguing hypothesis offers a potential answer. Increasingly, scientists think processed foods, with all their additives and sugar and lack of fiber, may be formulated in ways that disturb the gut microbiome, the trillions of diverse bacteria lining our intestines and colon. Those disturbances, in turn, may heighten the risk of chronic disease and encourage overeating.

The idea sheds new light on why ultraprocessed foods seem to be so bad for us. But to understand the hypothesis, we need to first look at what ultraprocessed foods are, and how they shape the community of bacteria in our gut that’s so intimately linked to our health.

Ultraprocessed foods, explained

More than half of the calories Americans consume now come from ultraprocessed foods. But what exactly are they?

For starters, ultraprocessed foods look a lot different from the foods our great-great-great-grandmothers ate, as author Michael Pollan would say. They’re the frozen chicken nuggets at McDonald’s, the soda and sports drinks in just about every beverage fountain across the country, and the milkshakes masquerading as coffee at Starbucks.

According to a widely used scientific definition, they’re:

industrial formulations made entirely or mostly from substances extracted from foods (oils, fats, sugar, starch, and proteins), derived from food constituents (hydrogenated fats and modified starch), or synthesized in laboratories from food substrates or other organic sources (flavor enhancers, colors, and several food additives used to make the product hyper-palatable).

In other words, ultraprocessed foods are created in factories. They’re pumped full of chemicals and other additives for color, flavor, texture, and shelf life. This processing generally increases the flavor and caloric density of the foods, while stripping away the fiber, vitamins, and nutrients. So these foods are distinct from whole foods (like apples and cucumbers) and processed foods (like vegetables pickled in brine, or canned fish in oil) that rely on only salt, sugar, and oil — rather than a range of complicated additives — to preserve them or make them tastier.

Read the rest of article at Vox